Intercalation between a well-characterized andisol fulvic acid and montmorillonite

The interaction of a well characterized fulvic acid, extracted from an Andisol, with a montmorillonite saturated with Na and Ca at pH 3.5 and 4.5 was studied. Experimental data showed that the FA can enter the interlayer of smectite at both pH values. Crystallite dimensions varied with the type of cation and influenced the amount of FA adsorbed. Only a small proportion of FA was tight to montmorillonite through a water bridge, the main type of bonding being constituted by a innersphere complex between the FA acid groups and the saturating cation.